Evidence obtained in this laboratory using mouse models suggests that lymphocytes, particularly thymus-derived lymphocytes, are important contributors to the severity of the lung disease which can be caused by influenza virus infection. This project is aimed at identifying the immunologic mechanisms influencing the development of the inflammatory response to this infection. Two virus derivatives of influenza A/Hong Kong virus which are equally infectious for mice but very different in their ability to cause pneumonia and death will be used. Indices of infection and inflammation will be correlated with the number, identity and functional competency of immunocytes from lung, thymus, spleen and peripheral nodes. Functional assays include lymphocyte-mediated cytotoxicity and blastogenic responsiveness to mitogens and antigens. Athymic nude mice develop little pneumonia when infected with virulent influenza virus, and the effect on this model of reconstitution with selected lymphocyte populations will be evaluated. The results of these studies and the contrast between the effects of infection with 2 different influenza virus derivatives should aid in defining the interactions and importance of immunopathologic processes in virus-induced inflammation of the lung.